Environmental Risk Arising From Well Construction Failure: Differences Between Barrier Failure and Well Failure, and Estimates of Failure Frequency Across Common Well Types, Locations and Well Age
- George Everette King (Apache Corp.) | Daniel E. King (WG Consulting)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 30 September-2 October, New Orleans, Louisiana, USA
- Publication Date
- Document Type
- Conference Paper
- 2013, Society of Petroleum Engineers
- 6.5.2 Water use, produced water discharge and disposal, 4.3.4 Scale, 5.2.2 Fluid Modeling, Equations of State, 2 Well Completion, 5.4.2 Gas Injection Methods, 6.5.3 Waste Management, 5.2 Reservoir Fluid Dynamics, 5.3.4 Integration of geomechanics in models, 1.14 Casing and Cementing, 3 Production and Well Operations, , 1.7.2 Managed Pressure Drilling, 7.2.1 Risk, Uncertainty and Risk Assessment, 5.4.6 Thermal Methods, 1.6 Drilling Operations, 1.14.3 Cement Formulation (Chemistry, Properties), 4.1.5 Processing Equipment, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 4.1.9 Tanks and storage systems, 4.2.3 Materials and Corrosion, 6.5.5 Oil and Chemical Spills, 4.1.2 Separation and Treating, 5.8.3 Coal Seam Gas, 4.2 Pipelines, Flowlines and Risers, 5.8.2 Shale Gas, 2.5.4 Multistage Fracturing, 5.1.1 Exploration, Development, Structural Geology, 1.7.5 Well Control, 1.7 Pressure Management, 4.6 Natural Gas, 1.6.11 Plugging and Abandonment, 5.8.5 Oil Sand, Oil Shale, Bitumen, 1.2.1 Wellbore integrity, 1.14.4 Cement and Bond Evaluation, 2.4.3 Sand/Solids Control, 2.2.2 Perforating, 4.5 Offshore Facilities and Subsea Systems
- Environmental, Well Integrity, Failure Estimates, Well Failure Risk, Barrier Failure Risk
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Do oil and gas wells leak to the environment? The great majority of wells do not pollute. The purpose of this paper is to explain basic concepts of well construction and illustrate differences between single barrier failure in multiple barrier well design and outright well integrity failure that could lead to pollution, using published investigations and reviews from data sets of over 600,000 wells worldwide. For US wells, while individual barrier failures (containment maintained and no pollution indicated) in a specific well group may range from very low to several percent (depending on geographical area, operator, era, well type and maintenance quality), actual well integrity failures are very rare. Well integrity failure is where all barriers fail and a leak is possible. True well integrity failure rates are two to three orders of magnitude lower than single barrier failure rates.
When a series of barriers fail and a leak path is formed, gas is the most common fluid lost. Common leak points are failed gaskets or valves at the surface and are easily and quickly repaired. If the failure is subsurface, an outward leak is uncommon due to lower pressure gradient in the well than in outside formations. Subsurface leaks in oil wells are rare and are routinely exterior formation salt water leaking into the well towards the lower pressure in the well.
Failure frequency numbers are estimated for wells in several specific sets of environmental conditions (location, geologic strata, produced fluid composition, soils, etc.). Accuracy of these numbers depends on a sufficient database of wells with documented failures, divided into: 1) barrier failures in a multiple barrier system that do not create pollution, and 2) well integrity failures that create a leak path, whether or not pollution is created. Estimated failure frequency is only for a specific set of wells operating under the same conditions with similar design and construction quality. Well age and era of construction are variables. There is absolutely no one-size-fits-all well failure frequency.
|File Size||1 MB||Number of Pages||29|